Some C# & F# code to talk about discriminated unions

case-block.cs

public enum LightSwith
{
    On,
    Dimmed(int intensity),
    Off
}

// And to use

var value = GetLightSwitchValue();
switch(value)
{
case On:
    TurnOnLight();
    break;
case Dimmed(intensity):
    DimLightToIntensity(intensity);
    break;
case Off:
    TurnOffLight();
    break;
}

case-lambda.cs

var value = GetLightSwitchValue();
switch(value)
{
case On:
    TurnOnLight();
    break;
case Dimmed(intensity) => 
    {
        DimLightToIntensity(intensity)
    }
case Off:
    TurnOffLight();
    break;
}

discriminated-union.fs

type LightSwith = 
| On
| Dimmed of int
| Off

And to use it, we use pattern matching:

let lightSwitch = getLightSwitchState()
match lightSwitch with
| On ->
    turnOnLight()
| Dimmed intensity -> dimLightToIntensity intensity
| Off -> 
    turnOffLight()

union.fs

type LightSwitch =
| On
| Off

// And to use it, we use pattern matching:

let lightSwitch = getLightSwitchState()
match lightSwitch with
| On ->
    turnOnLight()
| Off -> 
    turnOffLight()